Efforts are focused on the design, synthesis and evaluation of polypeptides that are targeted to inhibit, or otherwise modulate key cellular signal transduction processes. The long term goal is to develop effective agents that are selective in inhibiting the oncogenic cell proliferative signal, or to boost the effectiveness of tumor suppressor proteins, and thus could become useful cancer therapeutic agents. Design strategy includes evaluation of agents targeted to inhibit growth factor receptor interactions with secondary messenger proteins through their srs homology 2 (SH2) domain / tyrosine phosphorylated regions. Synthetic methodology was developed to incorporate various phosphatase resistant tyrosine-mimicking phosphonomethyl-phenylalanine analogs into key growth factor receptor autophosphorylation segment peptides. It was found that phosphono-difluoromethyl-phenylalanine (F2Pmp) containing peptides were the best inhibitors of autophosphorylation region / SH2 domain interactions. Such peptides bound to SH2 domains with good selectivity. One such peptide, on microinjection into insulin sensitized quiescent fibroblast cells inhibited cell cycle progression in response to growth factor stimulation. In another study, conducted in permeabilized T cells, peptides prepared with tandem F2Pmp amino acid building blocks were found to inhibit TCR-zeta / ZAP-70 interactions, and prevented TCR stimulated tyrosine phosphorylation of ZAP-70. In an unrelated study the mode of inhibition of cyclin dependent kinases by the p53 transcription product WAF1 is being examined. For this purpose the chemical synthesis of the entire WAF1 protein is undertaken, in segments of overlapping 20- to 25- mer peptides.